This invention relates to extruding, and more particularly to a new and improved method and apparatus for extruding thermoplastic polymer house siding.
In the extrusion process of thermoplastic materials, reliance is made on the die means for shaping the product from the extruder. In the manufacture of house siding, the extrudate is a relatively narrow width flat sheet of material having a turned over portion along one side edge to provide an interlock means. To handle this type of shape, the extrudate must be of high viscosity to prevent the distortion of the extrudate and prevent sagging of the siding in processing it. Cooling is generally done by air. The requirement of having a stiff melt in combination with the type of cooling generally applied would restrict the output to a range between 200 and 400 pounds per hour. The present invention provides a means for significantly increasing the extrusion rate by providing a method and apparatus for extruding the thermoplastic house siding at a higher temperature wherein the viscosity is relatively low by providing a novel shape and providing means for handling the low viscosity extrudate. By extruding the thermoplastic house siding in the form of a hollow rectangular shaped extrudate, then applying vacuum sizing techniques to it, has made it much easier to process, handle and size the thermoplastic siding. Since the melt can be processed at a higher temperature better properties such as high mechanical properties and excellent weathering characteristics can be developed in the material.